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Tall, multistory structures called skyscrapers are made of steel, which is sturdier and lighter in weight than other building materials, such as brick and stone. In the late 1800s, when steel production became common, architects experimented with steel, forming it into long, thin pieces called girders. The first skyscrapers, built in the United States in the 1880s, were constructed using vertical columns and horizontal beams made from steel girders. This supporting skeleton allowed buildings to rise to 10 or more stories. Skyscrapers grew taller when designers began using bundled steel tubes instead of heavy girders.

Tube buildings, like Chicago’s Sears Tower, get most of their support from a stiff grid of steel columns and beams in their outer walls. The lighter weight pieces need less support, and so architects can 144 add more height. Additional beams can be placed diagonally for additional support while adding little extra weight. The girders and beams are bolted together and welded on all sides so that the building will not sway from side to side as a unit when there is wind.

There are many cities around the world that are “big,” meaning they have more than 10 million people living in them. Tokyo, Japan, ranks the largest, since it has 33.2 million people living in the city, according to 2005 estimates. The next biggest cities in order of size are São Paulo, Brazil (17.7 million), Seoul-Incheon, South Korea (17.5 million), Mexico City, Mexico (17.4 million), Osaka-Kobe-Kyoto, Japan (16.4 million), and New York City (about 8 million people).

Most of these cities are located in different places around the globe. In the United States, after New York, Los Angeles is the biggest city (with almost 4 million people), and then Chicago (with almost three million people). Populations of cities are constantly changing as people move in and out of them, according to the U.S. Census Bureau, a government organization that estimates how big or small cities are based on their populations, or the number of people living in them.

The smallest dinosaurs were just slightly larger than a chicken. Compsognathus (meaning “pretty jaw”) was 3 feet (1 meter) long and probably weighed about 6.5 pounds (2.5 kilograms). At one time, scientists thought that Mussaurus (meaning “mouse lizard”) was the smallest dinosaur, but it is now known to be the hatchling of a dinosaur type that was much larger than Compsognathus when fully grown.

If birds are advanced dinosaurs, as some scientists believe, then the smallest dinosaur would be the hummingbird!

The expression dates back to the English Crown’s first efforts to control the Irish by outlawing their language and customs. But the unruly Irish were just that, and by the fifteenth century the English still controlled only a small area around Dublin, protected by a fortification called “The Pale,” meaning sharp sticks (i.e., impaled). To the British, to go “beyond The Pale” meant that you were entering the uncivilized realm of the wild Irish.

European settlers brought their money with them to America, and coins made of precious metal were accepted everywhere at face value. The Spanish peso was divided into eight silver coins, which the English called bits, or pieces of eight.

Two bits was one-quarter of a Spanish dollar. When money was printed and minted in the new world, although a dollar’s coinage was divided by ten, the expression “two bits” continued to mean one-quarter of a dollar.

A fruit is the part of the plant that nourishes and protects new seeds as they grow. The plant’s ovaries develop into fruit once the eggs inside have been fertilized by pollen. Some plants produce juicy fruit, such as peaches, pears, apples, lemons, and oranges.

Others produce dry fruit, such as nuts and pea pods. If an animal doesn’t eat the fruit, or a human doesn’t pick it off, it falls to the ground and decays and fertilizes the soil where a new seed will grow.

Earrings were used by seamen, especially warriors such as pirates, for very practical reasons and not for decoration. They were given to young sailors as a symbol of their first crossing of the equator, and their purpose was to protect the eardrums during battle.

The pirates, especially those who fired the ships’ cannons during closed combat with the enemy, dangled wads of wax from their earrings to use as earplugs.

Like many inventions, the development of the modern zipper can be traced to a series of events. In 1893, Whitcomb Judson patented and marketed a “clasp locker,” a complicated hook-and-eye shoe fastener. Together with businessman Colonel Lewis Walker, Whitcomb launched the Universal Fastener Company to manufacture the new device. He did not use the word “zipper,” although many people often credit him as the zipper’s creator. Instead, it was Swedish-born Gideon Sundback, an electrical engineer who was hired to work for the Universal Fastener Company, Who gets the credit.

He was responsible for improving Judson’s fastener, and by December 1913, he had designed the modern zipper. Sundback increased the number of fastening elements from four per inch to ten or eleven, had two facing-rows of teeth that pulled into a single piece by a slider, and increased the opening for the teeth guided by the slider. Sundback also created a machine that was able to manufacture the zipper.

There is no way specific way to place an order for a baby brother or a baby sister. The gender (boy or girl) of a baby is determined by whether the father’s fertilizing sperm has an X or a Y chromosome. An X chromosome will lead to a girl, and a Y to a boy. (Mothers always contribute an X chromosome.) Although scientific methods are available to help parents organize their chromosomes and take advantage of the fact that the “boy” sperm has less DNA than “girl” sperm, they can be expensive and unreliable. One method, called the Shettles method, recommends that if parents want a girl, they should plan to make a baby right around the time of ovulation.

At this time, the egg is as far away as possible from the incoming sperm so the long-distance runners of the sperm world, the X sperm, have a better chance of making it to the egg. For a boy, the method suggests that parents plan to make a baby about two to four days after ovulation. That way, the short-distance sprinting Y sperm can make it to the egg first. Many doctors say that although this method is based in science, it is no guarantee that a couple will have a baby boy or a baby girl.

A cactus-like plant of the lily family, aloe vera grows wild in Madagascar and on the African continent. It also is cultivated in Japan, the Caribbean, the Mediterranean, and the United States. People around the world have used its gooey, jelly-like sap for healing and cosmetic purposes.

Aloe extracts can be used to treat digestive problems, including constipation, and aloe oils are used in cosmetic creams to help keep skin soft and to treat minor skin irritations.